An observation post on Drigg beach. It was used by observers from the Eskmeals gunnery range a short distance down the coast, but looks to have been abandoned years ago. Photo: tim_d via Flickr.com.
Uranium particles formed from exploding DU munitions are highly persistent in the environment, scientists have found. They are still hazardous after 30 years in soils or dumps and even their corrosion products are durable minerals.
DU emerges as a long term pollutant in the environment whose very decay products serve to increase its persistence.
Campaigners have long argued that DU residues from conflict present a long-term risk to civilians.
This is due in part to the rate of radioactive decay from the isotopes in DU – and indeed DU gets more radioactive for thousands of years due to the in-growth of radioactive decay products.
But as two new studies reveal, it is also because of the rate at which DU dust particles and intact or fragmentary DU penetrators corrode in the environment – and the corrosion products.
To the horse’s mouth – the UK’s live DU firing ranges
The two UK studies have now shed more light on the processes that affect DU’s environmental persistence.
The studies were undertaken at the UK’s DU firing ranges. The first, ‘The corrosion of depleted uranium in terrestrial and marine environments’ by C. Toque et al, was performed at Kircudbright in Scotland, where DU rounds are fired into the sea.
The second, ‘Microanalytical X-ray Imaging of Depleted Uranium Speciation in Environmentally Aged Munitions Residues’ by Daniel E. Crean et al, was carried out at Eskmeals in Cumbria, England. Here DU was fired into hard targets to examine its effectiveness against different types of armour.
Eskmeals: considerable volumes of DU dust
The testing at Eskmeals produced considerable quantities of DU dust, some of which was found to have spread 6km from the site to the nearby village of Milom.
Researchers took samples of DU particles from two separate areas on the site and analysed them to assess how they had changed over the 30 years since they were first produced.
The two sites comprised an area of open surface soil, and a disposal area for DU-contaminated wood. “U speciation was different between the two areas”, the scientists found.
And given the high rainfall and oxidising conditions at the site, they may have been surprised to discover that:
“Surface soil particles showed little extent of alteration, with U speciated as oxides U3O7 and U3O8. Uranium oxidation state and crystalline phase mapping revealed these oxides occur as separate particles, reflecting heterogeneous formation conditions.”
Low DU solubility and mobility in soil
They conclude that “The persistence of U oxide phases such as U3O7 and U3O8 reﬂects the low solubility and mobility of the primary species in surface soils at the Eskmeals site.”
Furthermore, “the presence of primary impact particles results in the persistence of health risks associated with inhalation, should these particles be disturbed.”
No less surprisingly, “Particles recovered from the disposal area were substantially weathered, and U(VI) phosphate phases such as meta-ankoleite (K(UO2)(PO4)·3H2O) were dominant.
“Chemical imaging revealed domains of contrasting U oxidation state linked to the presence of both U3O7 and meta-ankoleite, indicating growth of a particle alteration layer.
However meta-ankoleite, a mineral also known as Hydrated Potassium Uranyl Phosphate, is highly insoluble under basic, neutral or mildly acidic conditions. The mineral’s formation indicates once again the persistence of DU in the environment.
“This study demonstrates that substantial alteration of DU residues can occur, which directly influences the health and environmental hazards posed by this contamination”, warn the researchers.
30 years, on, DU particles are still an inhalation hazard